package editdistance;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with this
 * work for additional information regarding copyright ownership. The ASF
 * licenses this file to You under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law
 * or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

import java.util.Arrays;

public class JaroWinklerDistance implements StringDistance
{

    private float threshold = 0.7f;

    private int[] matches(String s1, String s2)
    {
	String max, min;
	if (s1.length() > s2.length())
	{
	    max = s1;
	    min = s2;
	}
	else
	{
	    max = s2;
	    min = s1;
	}
	int range = Math.max(max.length() / 2 - 1, 0);
	int[] matchIndexes = new int[min.length()];
	Arrays.fill(matchIndexes, -1);
	boolean[] matchFlags = new boolean[max.length()];
	int matches = 0;
	for (int mi = 0; mi < min.length(); mi++)
	{
	    char c1 = min.charAt(mi);
	    for (int xi = Math.max(mi - range, 0), xn = Math.min(
		    mi + range + 1, max.length()); xi < xn; xi++)
	    {
		if (!matchFlags[xi] && c1 == max.charAt(xi))
		{
		    matchIndexes[mi] = xi;
		    matchFlags[xi] = true;
		    matches++;
		    break;
		}
	    }
	}
	char[] ms1 = new char[matches];
	char[] ms2 = new char[matches];
	for (int i = 0, si = 0; i < min.length(); i++)
	{
	    if (matchIndexes[i] != -1)
	    {
		ms1[si] = min.charAt(i);
		si++;
	    }
	}
	for (int i = 0, si = 0; i < max.length(); i++)
	{
	    if (matchFlags[i])
	    {
		ms2[si] = max.charAt(i);
		si++;
	    }
	}
	int transpositions = 0;
	for (int mi = 0; mi < ms1.length; mi++)
	{
	    if (ms1[mi] != ms2[mi])
	    {
		transpositions++;
	    }
	}
	int prefix = 0;
	for (int mi = 0; mi < min.length(); mi++)
	{
	    if (s1.charAt(mi) == s2.charAt(mi))
	    {
		prefix++;
	    }
	    else
	    {
		break;
	    }
	}
	return new int[]
	{ matches, transpositions / 2, prefix, max.length() };
    }

    public float getDistance(String s1, String s2)
    {
	int[] mtp = matches(s1, s2);
	float m = (float) mtp[0];
	if (m == 0)
	{
	    return 0f;
	}
	float j = ((m / s1.length() + m / s2.length() + (m - mtp[1]) / m)) / 3;
	float jw = j < getThreshold() ? j : j + Math.min(0.1f, 1f / mtp[3])
		* mtp[2] * (1 - j);
	return jw;
    }

    /**
     * Sets the threshold used to determine when Winkler bonus should be used.
     * Set to a negative value to get the Jaro distance.
     * 
     * @param threshold
     *            the new value of the threshold
     */
    public void setThreshold(float threshold)
    {
	this.threshold = threshold;
    }

    /**
     * Returns the current value of the threshold used for adding the Winkler
     * bonus. The deafult value is 0.7.
     * 
     * @return the current value of the threshold
     */
    public float getThreshold()
    {
	return threshold;
    }
}
